Many current communications systems transmit data across a subscriber loop communication line, referred to here in as a "subscriber line." The subscriber line is typically coupled to a communications network and to data communication equipment (DCE) at a customer's premises. For example, in the plain old telephone system (POTS), a subscriber line transfers data between a central office (CO) located within a public switched telephone network (PSTN) and a DCE, such as a modem or telephone, located at a customer's premises.
The PSTN is capable of supporting multiple types of communication signals. For example, the PSTN is designed to communicate voice signals associated with POTS communications, and the PSTN is also capable of data communication between data terminal equipment, such as computers, via the use of modems. T1 (1.544 Mbps) and Subrate Digital Service are other examples of data communication over the PSTN. Voice signals are typically communicated within a frequency band of 0 to 4 kilo-Hertz (KHz) while the frequency band of data signals vary with the type of data communication equipment utilized. However, data signals are frequently transmitted at frequency ranges much higher than the frequency band of voice signals. For example, data signals may be transmitted within a frequency range of 16 KHz to 80 KHz.
As known in the art, each end of the subscriber line should be terminated with a suitable impedance in order to enable communication of signals across the subscriber line. The amount of suitable impedance depends on the type of transmission medium and frequency band of the communication established on the subscriber line. For example, in voice signals associated with POTS communication, a relatively high termination impedance is desired while a relatively low termination impedance is desired for the communication of high frequency data signals. A typical termination impedance for POTS communication is between 600 and 900 Ohms, whereas a typical termination impedance for data communications within the 16 to 80 Klz band is approximately 135 Ohms.
Conventional communications networks usually terminate each end of the subscriber line with a single communications device. Therefore, the network utilizes conventional POTS splitters and POTS switches to route voice signals to POTS communications devices and to route data signals to data communications devices which support higher frequency ranges. Consequently, each communications device terminates its connection with a predetermined impedance suitable for the type and frequency band of communication supported by the communications device.
However, in order to increase the efficiency of data communication, it is desirable for each communications device to be capable of supporting either voice signals associated with POTS communication or of supporting data signals which communicate at higher frequencies. Accordingly, it is desirable for the communications device to adjust its termination impedance to correspond with the frequency band of the signals being communicated.
Thus, a heretofore unaddressed need exists in the industry for providing a system and method of varying an impedance of a communications device as a function of a frequency of the signals being communicated so that signals of different frequencies can be supported by the communications device.